1. Field of the Invention
The present invention relates to an apparatus and computer program for detecting a motion in an image frame and particularly to an improvement thereof wherein the motion detection is not affected by a change in illumination.
2. Description of the Related Art
There have been increased demands on security monitoring systems not only for industrial facilities, but also for small commercial facilities and ordinary families.
If the facility must be strictly observed, there are being arranged equipments and staffs for always watching the monitoring images. However, it is not easy for the commercial facilities and ordinary families to maintain strict observations.
Therefore, ordinary monitorings are executed in such a manner that automatic image recordings by a video tape recorder (VTR) or digital versatile disc (DVD) and automatic alarm generations are employed, only when a moving object such as an intruder is found out by a monitoring camera.
One of the image monitoring system employing a simplified motion detection apparatus is disclosed in JP11-39495A, 1999, pages 3-4 and FIGS. 2 and 3, wherein: an image frame is divided into a plurality of blocks; luminance or color signals are averaged every block; a difference between the present average and past average (average at several frames prior to the present frame) is compared every corresponding block; and it is determined that there is a motion if the difference is greater than a prescribed threshold.
However, the above mentioned conventional motion detection system has a disadvantage that an illumination change in the monitoring area may erroneously be determined to be a detected motion.
Here, the illumination change includes various examples such as a daylight change, turning on and off of lights at twilight or dawn and automobile lights shining into the monitoring area at night.
Further, flickers inevitably generated in video camera images may possibly be determined to be a detected motion.
Thus, the illumination change or flicker may be erroneously determined to be a detected motion in the conventional system as disclosed in JP11-39495A, 1999, because the motion is detected on the basis of the differences of luminance or color data between corresponding blocks in present and past frames.
Therefore, the above mentioned conventional system causes useless image recordings and alarms due to the erroneous motion detection, thereby inefficiently recording and searching images and causing a guard to rush to the monitoring spot, although it is not an emergency.
Although the erroneous motion detection may be reduced by an increased value of the prescribed threshold by which the motion is detected, a detection sensitivity becomes too lowered to accomplish a sufficient monitoring function.